Apparatus and method for venting and depressurization of an odorant injection system

ABSTRACT

The apparatus and method for venting and depressurization of an odorant injection system may be used on special LNG tankers that have onboard gasification equipment, on land or elsewhere. Odorant injection systems may operate at high pressures on an intermittent basis. On some occasions, the odorant is drained from a pressurized system and disposed of in inappropriate ways. The present invention depressurizes an odorant injection system and transfers the unwanted liquid odorant back into an odorant tank where it can be reused when the odorant injection system is restarted.

DESCRIPTION OF THE PRIOR ART

Natural gas is a clear, odorless and tasteless gas as it comes from theground. For safety purposes, odorant is commonly injected into thenatural gas before it is distributed to customers. There are many priorart odorant injection systems including U.S. Pat. No. 6,142,162 owned bythe assignee of the present application, which is incorporated herein byreference. Other odorant injection systems are disclosed in U.S. Pat.Nos. 5,406,970 and 6,208913 which are owned by Y-Z Industries, Inc.

On land, natural gas is commonly transported in pipelines. In order totransport natural gas in a ship, it is first liquefied and stored inlarge land based tanks before it is loaded onto the ship. One cubic footof liquefied natural gas (LNG) represents about 600 cubic feet ofnatural gas. Liquefaction saves space and makes LNG economical to shipon the high seas.

Natural gas is typically liquefied in geographic areas of the worldwhere natural gas is produced, but where there is little commercialmarket for the gas, such as Indonesia, Trinidad and the Middle East. LNGis commonly shipped on LNG tankers to markets where it is used, such asJapan, the United States and Europe. LNG it typically offloaded fromthese tankers to large tank based storage facilities on land where theLNG is gasified. Depending on local needs, the LNG may be gasified on acontinuous or intermittent basis.

Special LNG tankers have been developed which regasify the LNG onboardinstead of offloading the LNG to a large land based storage tank. Thesespecial LNG tankers often moor offshore to a buoy and gasify the LNGwhich is injected into a pipeline for transport to the pipelinedistribution grid onshore. This offshore gasification process may becontinuous or it may be intermittent; it make take several days togasify the LNG and empties the tanker.

Odorant injection systems are used on some of these special LNG tankerswith onboard gasification facilities. The onboard odorant injectionsystems need to depressurize between the intermittent periods ofgasification to reduce the chance of leaks and stress on the system.Leaks in odorant injection systems tend to have an in terrorium effectamong crew and officers because they sense a gas leak. There is a needfor improved systems to depressurize and vent odorant injection systemswhen not in use, such as between the intermittent periods ofgasification on special LNG vessels and elsewhere.

SUMMARY OF THE INVENTION

In the past, unwanted odorant has not always been treated with respect.For example, there are rumors that unwanted odorant has been collectedin a tin can or glass jug when an odorant injection system has beendepressurized. Other rumors indicate that unwanted odorant has sometimesbeen thrown on the ground or disposed of in other inappropriate ways.

The present invention is a system that returns unwanted odorant from adepressurized odorant injection system to an odorant tank(s) which issometimes called an odorant tote in the industry. The odorant can thusbe reused when the odorant injection system is restarted. The presentinvention also filters vapors from the odorant tank(s) before they arevented to atmosphere. If widely implemented, this system will reduceimproper disposal of odorant when an odorant injection system isdepressurized and it will reduce airborne discharge of stinky gas thathas a high concentration of odorant. The present invention may be usedonboard a LNG vessel and elsewhere.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an odorant injection system with flow arrowsindicating the odorant flow from the odorant tanks to and odorantinjection line.

FIG. 2 is a schematic of an odorant injection system with flow arrowsindicating the depressurization of the system and venting of filteredvapors to atmosphere.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic of an odorant injection system 10 with flow arrowsindicating the odorant flow from the odorant tanks 12 and 14 to theodorant injection conduit 16. This odorant injection system may belocated on a specialized LNG tanker, as previously described, or it maybe located elsewhere. For purposes of this illustration, the odorantinjection system 10 will be located on the specialized LNG tanker andwill be used to odorize the gasified LNG before it leaves the tanker.The regasification activity is intermittent.

A downcomer 18 is located in the first odorant tank and is in fluidcommunication with a valve 19, a conduit 20, a valve 22, a conduit 24, avalve 26, a conduit 28, a valve 30 and the first odorant filter 32.During the injection process, as illustrated by the flow arrows in FIG.1, liquid odorant 8 flows from the first odorant tank 14, through thedowncomer 18, the valve 19, the conduit 20, the valve 22, the conduit24, the valve 26, the conduit 28, the valve 30 to the first odorantfilter 32.

A second downcomer 34 is located in the second odorant tank and is influid communication with a valve 36, a conduit 38, a valve 40, a conduit42, the valve 26, a conduit 46, a valve 48 and the second odorant filter50. During the injection process, as illustrated by the flow arrows inFIG. 1, liquid odorant flows from the second odorant tank 14, throughthe second downcomer 34, the valve 30, the conduit 38, the valve 40, theconduit 42, the valve 26, the conduit 46, the valve 48 to the secondodorant filter 50.

It is typical for an odorant injection system to have dual filtration ofthe odorant as it flows from the odorant tank to the odorant pumps. Thefirst filter 32 is in fluid communication with valve 60, conduit 62, andthe common odorant feed conduit 64. The second filter 50 is in fluidcommunication with the valve 72, the conduit 73 and the common odorantfeed conduit 64. During the injection process, as illustrated by theflow arrows in FIG. 1, liquid odorant flows through the first odorantfilter 32 and the second odorant filter 50 through the common odorantfeed conduit 64, to the first odorant pump 70 and the second odorantpump 80.

As is well know to those skilled in the art, blanket pressure in therange of from about 20 psi to about 25 psi is kept on the first andsecond odorant tanks to help keep the conduits from the odorant tanks tothe odorant pumps at least partially filled with liquid odorant. Tankblanket pressure from the system cabinet, not shown, enters the systemthrough conduit 90 as indicated by the flow arrow. Blanket gas flowsthrough valve 92, tee, 96, valve 98, conduit 100, valve 102 and into thetop of the first odorant tank 12. Blanket gas flows through the valve92, the tee, 96, the valve 104, the conduit 106 and the valve 108 to thetop of the second odorant tank 14. Because blanket gas is relatively lowin pressure, leaks in the odorant injection system seldom developbetween the odorant tanks and the injection pumps. However, downstreamof the odorant pumps, the odorant may reach pressures in the range ofabout 1400 psi. These relatively higher pressures, especially those inthe odorant injection conduit 16 may cause leaks; it is thereforedesirable to depressurize the odorant injection conduit 16 when not inuse.

Odorant 8 is pressurized in the first pump 70 and exits the first pumpat the outlet 120 and passes through conduit 122, a valve 124, a conduit126, a tee 128, a valve 78 and enters a flowmeter 132. Likewise, odorant8 is pressurized in the second pump 80 exits the second pump 80 at theoutlet 134, and passes through a conduit 136, a valve 138, the tee 158,the valve 130 and enters the flowmeter 132.

Odorant 8 exits the flowmeter 132 through a flowmeter outlet 142 andpasses through a valve 144, a conduit 146, a check valve 148, a conduit150, a valve 152 and enters the odorant injection conduit 16.

FIG. 2 is a schematic of an odorant injection system with flow arrowsindicating the depressurization of the system and venting of filteredvapors to atmosphere. The structure depicted in FIG. 1 and FIG. 2 is thesame, but the flow of odorant through FIG. 1 is the opposite of the flowthrough FIG. 2 as indicated by the flow arrows in each respectivefigure. In FIG. 1, the odorant injection system 10 is pumping liquidodorant into the odorant injection conduit 16. In FIG. 2, the odorantdepressurization system 160 is depressurizing the odorant injectionconduit 16 and venting filtered vapors to atmosphere. The odorantdepressurization system 160 is composed generally of the bypass conduit162, the vapor filter 164, and valves which will be described in detailbelow.

During depressurization odorant flows from the odorant injection conduit16 through the valve 152, a conduit 167, a valve 166, the bypass conduit162, a valve 168, and into a tee 169 where the flow splits and passesthrough the valve 22, the conduit 20, the valve 19, the downcomer 18 andback into odorant tank 1. Odorant from the tee 169 also passes throughthe valve 40, the conduit 38, the valve 30 and the downcomer 34 into thesecond odorant tank 14.

Vapors 6 from the first odorant tank 12 pass through the valve 102, theconduit 100, the valve 98, a tee 178, a valve 170, a conduit 172 andinto the vapor filter 164, as indicated by the flow arrows. Vapors 6from the second odorant tank 14 pass through the valve 108, the conduit106, a valve 104, the tee 178 and merge with the stream from the firstodorant tank. The combined flow of vapors passes through the valve 170,the conduit 172 and into the vapor filter 164. Filter media, not shown,fills the inside of the vapor filter. Activated charcoal is a suitablefilter media. Other types of filter media may be used or several typesof media may be used in the vapor filter. After passing through thefilter media, the filtered vapors 175 exit the vapor filter 164 at theexit port 174 as indicated by the flow arrow. The filtered vapors 175have a lower concentration of odorant than those exiting the odoranttanks, 12 and 14.

Operational Description of FIGS. 1 and 2

Referring to FIG. 1, the purpose of the odorant injection system 10 isto inject odorant 8 from the tanks 12 and 14, under pressure into theodorant injection conduit 16. In FIG. 1, the following valves are in theopen position during injection of odorant: 19, 22, 26, 30, 32, 48, 60,68, 72, 92, 98, 102, 104, 108, 124, 130, 144, 152. In FIG. 1, thefollowing valves are in the closed position during injection of odorant:166, 168, 170 and 176. Odorant flows from the odorant tanks, the odorantfilters, the odorant pumps, the odorant flowmeter to the odorantinjection line as indicated by the by the flow arrows in FIG. 1.

Referring to FIG. 2, the purpose of the depressurization system 160 isto depressurize the odorant injection line 16, transfer unwanted odorantback into the odorant tanks 12 and 14 and vent purified vapors toatmosphere. In FIG. 2, the following valves are in the open positionduring the depressurization of the odorant injection system: 19, 22, 98,102, 104, 108, 152, 166, 168, and 170. In FIG. 2 the following valvesare in the closed position: 26, 130, 144 and 176 as indicated by the bythe flow arrows in FIG. 1. The odorant flows from the odorant injectionline, through the bypass line to the odorant tanks, as indicated by theby the flow arrows in FIG. 1. Vapors leave the odorant tanks, passthrough the filter and are vented to atmosphere as indicated by the flowarrows in FIG. 1.

As an example, the present invention is capable of depressurizing a ¾inch odorant injection line that is approximately 600 feet long from theodorant injection system cabinet, not shown, to the point of injectioninto the gas being offloaded from the LNG ship. A typical odorant totemay hold 250 gallons of odorant so the tote may weigh more than 1700lbs. Heavy items like the odorant tote need to be lifted from sea levelto the deck of the LNG tanker by an on-board crane. Two totes are oftenused in the odorant injection system. The deck of the LNG tanker isabout 3 stories from sea level. The odorant injection system cabinetneeds to be near the totes, which need to be near the crane. Thislocation necessitates a long odorant injection line that is severalhundred feet in length. The present invention can reduce the pressure inthe odorant injection line from about 1400 psi to about zero psig. Afterdepressurization, it takes some odorant systems about 15 to about 20minutes to build up the necessary pressure in the aforementioned odorantinjection line, before offloading can begin. Odorant is not put in LNGbecause it can crystallize.

Odorant injection systems are often controlled by a programmable logiccontroller (PLC), personal computer (PC), flow computer or otherautomated means that is often housed in the odorant injection cabinet,as is well know to those skilled in the art. The PLC, PC, flow computeror other automated means controls the operation of the odorant injectionpumps, valves and other necessary components to control the injectionsystem. The PLC, PC, flow computer or other automated means may also beused to control the valves in the present invention. In the alternative,the present invention may be manually operated.

1. An odorant depressurization system for depressurizing at least aportion of an odorant injection system in an environmentally friendlymanner, the odorant injection system having at least one odorantinjection pump, at least one odorant container and at least one odorantinjection conduit in fluid communication with the at least one odorantinjection pump and at least one natural gas conduit, the odorantdepressurization system comprising: at least one bypass conduit in fluidcommunication with the odorant injection conduit and the at least oneodorant container; at least one vapor filter in fluid communication withthe at least one odorant container and atmosphere; a plurality of valvesto open the bypass conduit to fluid communication from the odorantinjection conduit to the at least one odorant container and to close thebypass injection conduit to fluid communication with other portions ofthe odorant injection system; and a plurality of valves to open the atleast at least one vapor filter to fluid communication from the at leastone odorant container and to open the at least one vapor filter toatmosphere to vent purified vapor from the at least one odorantcontainer.
 2. A system for venting vapors from an odorant injectionsystem to atmosphere, said vapors having a reduced concentration ofodorant, the venting system comprising: means for transporting odorantfrom an odorant injection conduit into an odorant container, thetransporting means including valving to selectively direct the flow ofodorant from the injection conduit into the odorant container; and meansfor filtering vapor from the odorant tank to reduce the concentration ofodorant in said vapor before it is vented to atmosphere, the filtermeans including valving to selectively direct the flow of vapors fromthe odorant container, through the filter means and thereafter into theatmosphere.
 3. A method for venting vapors and depressurization of anodorant injection line comprising the following steps: depressurizingthe odorant injection line and allowing the odorant in the odorantinjection line to flow back into an odorant container; and venting theodorant container and filtering the vapors that are vented to reduce theconcentration of odorant in the vapors before said vapors are vented toatmosphere.
 4. In combination, an odorant injection system withintegrated depressurization system for use on an LNG tanker with onboardgasification systems, the odorant injection system with integrateddepressurization system including: an odorant injection system having;at least one odorant storage tank to contain a supply of liquid odorant;at least one odorant injection conduit; at least one odorant injectionpump to pump liquid odorant from the at least one odorant storage tankto the at least one odorant injection conduit; and conduits providing afluid flow path between the at least one odorant storage tank, the atleast one odorant injection pump and the at least one odorant injectionconduit; an odorant depressurization and venting system having; a bypassline to drain liquid odorant from the at least one odorant injectionconduit into the at least one odorant storage tank; a vapor filter topurify vapors from the at least one odorant storage tank, before thevapors are vented to atmosphere; means for controlling the odorantinjection system and odorant depressurization system including valves todirect the liquid odorant flow path into the at least one odorantinjection conduit when the system is injecting odorant and to direct theliquid odorant from the at least one odorant injection conduit to the atleast one odorant storage tank when the system is being depressurized.